Purpose
Miller's is the most commonly used classification of gingival tissue recessions. However, data on the reliability of this classification are missing so far, although reliability, which reflects the consistency of repeated measurements, is regarded as a prerequisite for judging the utility of a classification. The primary aim of the present study was to determine inter- and intra-observer agreement on Miller’s classification. Second, 3 additional parameters, associated with gingival tissue recessions, were evaluated.
Methods
Two hundred photographs (50 of each region: maxillary/mandibular anterior/posterior teeth) of gingival tissue recessions were evaluated twice (interval of one month) by 4 observers in Miller's classification (classes I to IV), gingival phenotype (thin&high or thick&low scalloping), tooth shape (long-narrow or short-wide), and identifiability of the cemento-enamel junction (CEJ). The level of agreement was assessed according to a 6-level nomenclature: poor <0.0, slight 0.0-0.2, fair 0.21-0.4, moderate 0.41-0.6, substantial 0.61-0.8, almost perfect 0.81-1.0.
Results
The inter- and intra-observer agreements on the assessed parameters are summarised in the table. The inter-observer agreement on Miller's classification was substantial, with the highest values for anterior teeth. The intra-observer agreement was substantial to almost perfect, with the highest values for maxillary anterior teeth. The differences between the first and second ratings as well as among the different observers were mainly among Miller’s classes I, II, and III, but never between classes I and IV.
The inter-observer agreement on the gingival phenotype was slight to moderate, with higher values for anterior mandibular teeth. Similar results were seen for intra-observer agreements. In general, the intra-observer agreements for all regions were moderate for each observer.
The inter-observer agreement on tooth shape was fair to moderate, with higher values for the anterior mandibular teeth. Similar results are presented for intra-observer agreement. In general, intra-observer agreement for all regions was moderate for each observer.
Inter-observer agreement on the identifiability of the CEJ was slight to fair, with values just slightly higher for anterior teeth. Intra-observer agreement was poor to almost perfect. The anterior mandibular teeth presented slightly higher values.
Gingival phenotype (thin-high scalloping) significantly correlated with tooth shape (long-narrow) (rho=0.662, p<0.001). Anterior teeth presented a higher correlation, with the mandibular anterior teeth presenting an almost perfect correlation (rho=0.954).
Conclusions
Miller’s classification of gingival tissue recessions was evaluated by 4 examiners using 200 photographs and yielded substantial to almost perfect agreement, with higher agreement for anterior teeth. The present study offers the so far missing proof on the sufficient inter- and intra-observer agreement of this classification.